Synchronous Buck Controller for
Dynamic Load-Voltage Applications
POWER MANAGEMENT
Description
The SC470 is a single output, constant on-time
synchronous-buck, pseudo-fixed frequency, PWM
controller intended for use in notebook computers and
other battery operated portable devices. Features
include high efficiency and fast dynamic response with
no minimum on-time. The excellent transient response
means that SC470 based solutions will require less
output capacitance than competing fixed frequency
converters.
The SC470 is specifically targeted for graphics processor
power supplies that require dynamic voltage transition,
with a tight 0.85% DC accuracy and a 20% OVP threshold.
The frequency is constant until a step-in load or line
voltage occurs, at which time the pulse density and
frequency will increase or decrease to counter the change
in output or input voltage. After the transient event, the
controller frequency will return to steady state operation.
At light loads, Power-Save Mode enables the SC470 to
skip PWM pulses for better efficiency.
The output voltage can be adjusted from 0.5V to VCCA.
The integrated gate drivers feature adaptive shoot-
through protection and soft switching. Additional features
include cycle-by-cycle current limit, digital soft-start, over-
voltage and under-voltage protection, and a PGD output.
SC470
Features
Constant on-time for fast dynamic response
Programmable VOUT range = 0.5 – VCCA
VBAT range = 1.8V – 25V
DC current sense using low-side RDS(ON) sensing
or RSENSE in source of low-side MOSFET for
greater accuracy
Resistor programmable on-time
Cycle-by-cycle current limit
Digital soft-start
Combined EN and PSAVE functions
Over-voltage/under-voltage fault protection
and PGD output
20% OVP threshold for simpler dynamic voltage
transition circuitry
5µA typical shutdown current
Low quiescent power dissipation
14 lead TSSOP and 16 pin MLPQ (4mm x 4mm)
packages
Industrial temperature range
0.85% DC accuracy
Integrated gate drivers with soft-switching
Applications
Graphics Cards
Embedded Graphics Processors
High Performance Processors
Typical Application Circuit
VBAT
5VSUS
5VSUS
VBAT
D1
R1
RTON
R1
10R
U1
EN/PSV
TON
VOUT
R2
VCCA
R2
FB
PGOOD
R4
PGD
VSSA
VDDP
DL
C4
C6
1uF
PGND
1uF
Q2
ILIM
+
VOUT
SC470
BST
DH
LX
R3
C1
0.1uF
Q1
C2
10uF
L1
VOUT
C3
C5
1nF
September 27, 2005
1
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